Strap and method for producing same

ABSTRACT

A method of fabricating an inflatable seat webbing, more particularly for a seat belt, comprising the steps of weaving a two-ply fabric having an upper ply and a lower ply, folding and placing outermost outer parts on adjoining parts so that all parts are located in sequence above or below a middle part to result in, as viewed in a warp direction, the configuration of a collapsed concertina, and tucking the middle part to the left as viewed from a predetermined direction in relation to fabric threads so that the upper ply and the lower ply of the middle part formerly facing each other now face outwards and sandwiching the folded outer parts and the middle part in between.

The invention relates to a method of fabricating a woven, inflatablewebbing, more particularly an automotive seat belt webbing.

Known from German Patent 20 08 048 (Rutzki) is a webbing configuredtubular and comprising a portionally stitched burst fold designed toburst open due to the tensional forces exerted by the belt in acollision whilst activating opening of a valve connected thereto toinflate the tubular belt portionally, as a result of which the beltlocated as a flat tube prior to the accident, the width of whichcorresponds to half the circumference of the inflated belt, isexplodingly inflated portionally. It thus represents an “impact cushion”of advantage to a certain extent as compared to the straight-forwardbelt. However, adequate protection of the vehicle occupant fails to besatisfactorily assured due to the insignificant extent of theportionally inflated tubular belt. Increasing the circumference of thebelt tube cited likewise in the same document with an inflatablecushion, arranged portionally about the belt also has its disadvantagessince the corresponding cushion is not necessarily correctly located inan emergency situation and thus actually fails to be available for itsintended purpose.

Known from the international patent application PCT/US95/10695 (Simula)is a inflatable, tubular restraint system. The seat belt system evidenttherefrom consists of a lap belt and a shoulder belt, the lap beltconsisting portionally of an inflated balloon which during inflation isshortened in length to thus have a belt tensioning function in additionto its impact cushioning function. Although in this arrangement theabdominal zone of the vehicle occupant is particularly protected, noprotection is given to the shoulder and head zone, however, except foran additional restraint of the shoulders by the tensioned belt.

The object of the invention is to provide a belt or webbing as well as amethod of fabricating same having practically no limitations, i.e. inassuring optimum impact protection irrespective of the actual locationin an accident situation and permitting cost-effective and reliablefabrication of the webbing respectively.

This object is achieved by a method as it reads from claim 1 and/or amethod as it reads from claim 2 and a webbing as set forth in claim 5.

The method in accordance with the invention for fabricating a webbingcomprises (in short) the following steps, weaving a two-ply (upper orfirst ply, lower or second ply) three or more part (at least one leftouter part, middle part, at least one right outer pan) fabric,concertina folding and placement of more than two outer parts, form eachoutermost outer part to each innermost outer part until the no more thantwo outer parts are located on the outer parts adjoining note middlepart, folding the one outer part adjoining the middle part along the onecrease onto an outer surface of the middle part facing away from thesecond ply, folding the other outer part along the other crease onto theother outer surface of the middle part facing away from the firs ply sothat—as viewed in the warp direction—the configuration of a collapsedconcertina materializes and tucking the middle part “to the left” sothat the one and other surface of the middle part formally facing awayfrom each other now face each other and sandwich the folded outer parts.

With a webbing fabricated in this way any webbing/air bag configurationis optionally achievable to advantage. Depending on the selected numberof outer parts an air bag volume achievable by the air bag belt beinginflated as prompted by the collision materializes differing in size,thus permitting adaptation to all differences in vehicle type, seatingconfiguration, occupant stature, body weight to be cushioned, etc.Another advantage is that by additionally nip seaming the outer partsindividually from the edges—outermost in the woven condition—inwards tothe middle part a belt bag volume is attainable which is uneven in thelongitudinal direction of the webbing (FIGS. 6 to 8 and 10). As a resultof this it is now possible to save having to provide the side air bagusually accommodated in the door cladding and the head bag usuallyaccommodated in the roof ledge above the doors. The vehicle occupant issafeguarded by a sole air bag integrated in the seat belt, i.e. by abelt bag in lap, flank, chest and head zone and protected from injury byimpacting vehicle parts, irrespective of his posture, i.e. whetherrelaxed, slumped or sitting upright. One particular advantage of themethod in accordance with the invention and thus of the webbingfabricated thereby is in it saving several expensive air bag systems (atleast one door air bag and 1 side/head air bag per vehicle occupant).Nip seaming as mentioned above is not restricted to actual stitching,i.e. seaming, this instead intended to mean all measures undertakensuitable for individually locally joining the top with the bottom fabricply such as weaving, bonding, welding and the like. It is particularlyof advantage and cost-saving to fabricate the nip seam(s) by selectivelyweaving the top to the bottom fabric ply on a Jacquard weaving machine.

The method in accordance with the invention for fabricating a webbingcomprises (in short) the following steps: weaving a two-ply (upper ply,lower ply) three-part (left outer part, middle part, right outer pant)fabric, folding the one outer part along a crease onto the surface ofthe middle part, folding the other outer part along the other creaseonto the other surface of the middle part so that—as viewed in the warpdirection—the configuration of a collapsed Z materializes and tuckingthe middle part “to the left” so that the one and other surface of themiddle pant formerly facing away from each other now face each other andsandwich the folded outer parts.

Weaving may be implemented on a Jacquard wide web weaving machine or aneedle web weaving machine. Folding the outer parts is done on simplemeans suitable for this purpose which are not described further. Tuckingthe middle part “to the left” is done by introducing a rod or the liketipped with a gripper into a matched length of webbing between the twomiddle part plies until the gripper reappears at the other open end ofthe webbing and clamps in the gripper the middle parts folded inwardstogether with the outer parts folded thereon and then withdrawing therod together with the gripper contrary to the direction inserted fromthe interior of the middle part with a suitable counterhold. Once therod with the gripper is fully withdrawn a fully “left-hand” tuckedwebbing is available in which the outer parts are sandwiched betweenfabric plies of the middle part. The method in accordance with theinvention is thus an advantage because it is so simple and producessmooth webbings.

The weft thread of the webbing in accordance with the invention may be asole multifil or a multifil with a monofil. Employing monofil as theweft thread results in a stiffer, more elastic webbing. Logos and thelike may be, of course, included in the weave of the webbing inaccordance with the invention by suitable setting the shanks and shankcontrol, there being no limits to that desired by the user in thisrespect.

One advantageous further embodiment of the method in accordance with theinvention reads from claim 2, it being here in particularly that thewarp threads in the region of the narrow creases have a dtex roughlyhalf that of the warp threads of the middle part. If, for example, thewarp threads of the middle part are dtex 1100, then the warp threads ofthe narrow creases are dtex 550. This brings the advantage that in thefolded condition in which, as viewed in all, the material of the creasesis present in four plies, as compared to the double ply of the middlepart, a more or less equal thickness of the folded webbing results overthe full width since the warp threads in the creases are roughly half asthick as the warp threads in the middle part.

In a further advantageous aspect of the invention the two fabric pliesin the middle portion of the middle part are joined to at least twoburst threads running substantially in the warp direction.

In another advantageous aspect of the invention the fabric of thewebbing is provided with a coating prior to folding. The coating resultsin a significant reduction in the permeability of the fabric and enablesthe internal pressure of an inflated webbing to be maintained over alonger period in time. This is particularly decisive when the vehicle isnot abruptly halted by a collision, it instead toppling or continuingits travel so that the vehicle occupant needs to be safely restrained inthe vehicle seat correspondingly longer.

Advantageous further embodiments and features of the invention read fromthe sub-claims.

The invention will now be detailled with reference to the attacheddrawings to which reference is made and in which:

FIG. 1 is a schematic viewed in perspective of a webbing in accordancewith the invention after the “weaving” step in the method.

FIG. 2 is a section through the detail X as shown in FIG. 1 on amagnified scale.

FIGS. 3a to 3 c is a strongly schematic view of the webbing inaccordance with the invention as shown in FIG. 2 illustrated before,during and after folding the outer parts.

FIG. 4 is a schematic view of the webbing in accordance with theinvention shown greatly magnified as shown in FIGS. 3a to 3 c after the“tucking” step in the method.

FIG. 5 is a schematic view as seen from above of a section of thewebbing in accordance with the invention (as shown in FIG. 1).

FIG. 6 is a further embodiment of the webbing fabricated by the method.

FIG. 7 is a further embodiment of the webbing fabricated by the method.

FIG. 8 is a further embodiment of the webbing fabricated by the method.

FIG. 9 is a schematic illustration of a matched woven webbing includingtwo outer parts each and a middle part.

FIG. 10 is a schematic illustration of how the outer parts are folded insequence up to finally on the middle part.

Referring now to FIG. 1 there is illustrated a webbing 1 after weavingwith the two fabric plies “upper ply” O and “lower ply” U each dividedin turn into three roughly equal parts “left outer part” LA, “middlepart” M and “right outer part” RA. The thickness of each warp threadrunning in the direction of the arrow K and the individual warp threadsare indicated only schematically to simplify the illustration. It isevident in the middle part M that the warp threads are substantiallythicker than the warp threads in the outer parts LA and RA. On theleft-hand side of the left outer part the upper fabric ply O and thelower fabric ply U are interwoven. This portion is identified by thereference letters LK. Located opposite thereto there is an edge LR alongwhich the right outer parts RA of the upper fabric ply O and of thelower fabric ply U are interwoven. In the transition portion from themiddle part M to the outer parts RA and LA creases FZ are evident inwhich the warp threads are finer than in the middle part M and coarserthan in the outer parts LA and RA. The detail X is illustrated magnifiedin FIG. 2 and further described. The webbing is leaving the loom asshown in FIG. 1.

Referring now to FIG. 2 there is illustrated schematically the detail Xtaken from FIG, 1, here greatly magnified, to show the differences inthe thickness of the warp threads. Evident on the left-hand side is theleft edge LK along which the upper fabric ply O and the lower fabric plyU are interwoven. Evident in sequence from the left outer side of thewoven webbing up to the centerline showed on the right hand side in FIG.2 are the following portions of the webbing: on tile left-hand side isthe left outer part LA adjoining the left crease FZ which in turn ittraslates into the middle part M. In this example embodiment it is notthe individual warps that are shown but in their thickness through thewebbing thickness illustrated as a strip. The differing warp threaddiameters are clearly evident from the example embodiment as shown inFIG. 2. Thus, for example, the diameter of the warp threads in the leftouter part is roughly a tenth of that of the warp thread in the middlepart. In the crease FZ the diameter of the warp thread is roughly halfmat of the warp threads in the region of the middle part M. Theadvantages or differing functional assignments of these differences inthe warp threads are evident in detail from the description of FIG. 4.Roughly in the middle of the crease FZ, but possibly shifted alsosomewhat nearer to the middle part M, is indicated the position of aburst thread AF illustrated schematically interconnecting the upperfabric ply O and the lower fabric ply U and designed to burst at apredetermined rupture load so that the individual fabric plies move inthe direction of the explosion arrows E (FIG. 4) and opening the webbinginto an inflated belt ba& For the application in which the material ofthe outer parts LA and RA is selected thicker, the position of the burstthreads AF (FIG. 4) may also be displaced somewhat inwards toaccommodate the heavier coverage In this case, namely, the upper and thelower fabric ply may slightly depart from each other since the fabric isable to yield slightly in the creases (upwards and downwards in FIG. 4).

Referring now to FIGS. 3a to 3 c there is illustrated schematically howthe outer parts are folded onto the middle part. To simplify theillustration the differences in the diameter of the warp threads are nottaken into account, i.e. in the FIGS. 3a to 3 c all of the warp threadsare depicted schematically with the same diameter. FIG. 3a shows thefabric parts LA, M and RA still to be folded. In FIG. 3b the left outerpart LA has been folded onto the middle part M in the middle. At thesame time FIG. 3b shows on the right-hand side the direction arrowindicating the folding direction of the right outer part RA. In thisillustration the reference letters FZ indicate the location of thecreases FZ. FIG. 3c shows the webbing after the outer parts have beenfolded. Otherwise it is irrelevant whether the left outer part LA islocated at the top and the right outer part RA on the bottom of themiddle part, it being just as possible to make the folds in the reversedirection. The folding configuration as shown in FIG. 3c results in anS-shape in principle. The reverse folding direction would produce a Zshape, there being, as said, no difference in this respect. Themagnified illustration as shown in FIG. 4 relates in this respect to afolding direction producing a Z-shaped configuration.

Referring now to FIG. 4 there is illustrated schematically the actualdifferences in diameter of the warp threads greatly magnified. It is inthis simplified schematic illustration that the webbing in accordancewith the invention is evident after having been tucked “to the left”.Again evident is the middle part M illustrated discontinued in themiddle, as well as the left-hand crease FZ. Since the webbing 1 inaccordance with the invention is configured symmetrically about thecenterline or point PS FIG. 4 is identified by reference letterssubstantially on one side only. It is obvious, of course, thatillustrating the actual configuration of the tucked webbing is notpossible in FIG. 4, because the cavities H shown therein to be seen forexample in the region of the burst thread or in the inverse positionsare not present in reality, since namely after being tucked the webbingis ironed or flattened and fixed in some other way. This results in eachmaterial “seeking” an available space so that an optimally dense packageis achieved. Depicting this in the illustration is, for one thing,extremely difficult and, for another, it would hardly furnish any stilluseful information.

Evident on the left-hand side of FIG. 4 is an additional burst threadZRF which joins the folded fabric plies to each other in the crease FZ.This version could be put to use when wishing to avoid any “bloating” ofan inlaid voluminous inlet with the intention of obtaining a morecompact webbing.

Referring now to FIG. 5 there is illustrated schematically a section ofa webbing in accordance with the invention as seen from above. Indicatedin the middle part of the webbing are two broken lines SF defining theposition of optimum nip seams for the supply gas hose. These nip seamsmay be stitched in place along the webbing when tucked by means of asewing machine. The so-called supply gas hose is inserted between thetwo nip seams for supplying the webbing with explosion gas whenexplosion is called for.

Referring now to FIG. 6 there is illustrated an example embodiment ofthe invention fabricated by the method as it reads from claim 10. Thisdrawing is strongly schematic to simplify the illustration, it showingnot the final product but various stages in the method and their specialfeatures. Thus, in this case what is shown in principle is a seat beltprepared for being assembled into a seat belt module. The salientfeature of this seat belt is that it has a portion in which it isinflatable (ABB) and a portion in which it is intended for being rolledup in a retractor (ARB). As a result, the seat belt is thinner in theretraction portion ARB than in the inflation portion ABB. Shown in theupper part of FIG. 6 is the inflation portion ABB shown in earlierexample embodiments of the webbing in accordance with the invention withthe middle part M and the outer parts LA and RA as well as the burstseam AF running in the creases as known from the above description. Whena predetermined length is cut off from an endless webbing woven in thiskind the retraction portions ARB and inflation portion ABB abutting eachother at a line QL are defined. After this, the transverse seams LSN andRSN are applied to the outer parts of the webbing in line with QL bymeans of a sewing means. These seams are sealing seams and close off theweb plies of the outer parts sealingly. Before or after applying thetransverse seams LSN and RSN the longitudinal seams 3 and 11 are appliedwhich extend along the retraction portion ARB. In both the left-hand andright-hand outer part together with the outer edges of the webbing andthe edges marked previously with the scissor lines the seams LSN, RSN, 3and 11 surround portions AS, each of which is depicted schematically bya double dot/dash line. When these portions AS are cut out, theremaining outer parts LA and RA, as already described before for otherexample embodiments, especially with reference to the FIGS. 3a, 3 b and3 c, are folded in Z-shape and the complete webbing tucked to the leftin accordance with the step in the method “tucking the middle part”.This results in a portion in which with the air bag fabric tuckedinwards produces the inflation portion whilst the webbing tucked intothe retraction portion ARB contains no bag fabric as such. Then, themiddle part M of the webbing is sealed gas-tight along the line QL by amiddle seam MN, thus resulting in a webbing ready for assembly in moduleproduction.

Referring now to FIG. 7 there is illustrated an embodiment of a webbingin accordance with the invention substantially the same as the versionshown in FIG. 6 except that, as the main difference, there after weavingno seams are placed to join the upper and lower woven ply of the outerparts. Instead, joining the upper and lower woven ply in this portion iscreated along a transverse line QL already during weaving, namely by theupper ply and the lower ply of the outer parts LA and RA of the webbingbeing interwoven in a strip by means of transverse seams 7 and 9 runningin the weft direction, thus resulting in a positive connection of theupper and lower woven ply already during weaving. The same interweave isalso intended along the creases in the retraction portion so that a firmconnection of the upper and lower woven ply is produced during weavingin the strips 5 and 11 along the creases. These joining portions of theupper and lower woven ply indicated symbolically by cross-hatchingreplace the longitudinal and transverse seams applied in the exampleembodiment as shown in FIG. 6. The further handling of the webbing up toits condition ready for assembling in the module is the same asdescribed relative to the FIG. 6 to which reference is accordingly made.In the example embodiments as shown in FIGS. 6 and 7 no burst seam AF isneeded in the portion ARB.

Referring now to FIG. 8 there is illustrated schematically an exampleembodiment of a webbing produced by the method. Evident in the upperpart of FIG. 8 is a webbing in accordance with the invention alreadytucked so that the outer parts LA and RA are located inwards. A webbing13 is inserted (in FIG. 8 from below) into the interior of the tuckedwebbing, i.e. into the middle plane indicated by an arrow ME between thetucked-in outer parts LA and RA over a length ES intended to designatethe length of an end portion of the inserted webbing 13. For the sake ofsimplicity the differing thicknesses in the fabric are not indicated bydiffering line thicknesses, a uniform line thickness being usedthroughout. However, from the description relative to the FIGS. 2 and 4in particular, it is obvious that significant differences in fabricthicknesses exists After having sandwiched the single-ply a webbing 13between the two plies of the two-ply fabric there are stitched by one ormore seams VN, spaced away from each other sufficiently so that theoverlapping portion ESB of the plies remaining floppy. It will readilybe appreciated that the four transverse seams VN in the exampleembodiment as shown in FIG. 8 do not detriment of floppiness of thetransition portion RB of the webbing. The number of four seams VNselected in this case and also the end portion EB or its length areselected merely as an example. Depending on the user specification theend portion or it length/width ratio maybe other the that as shown inFIG. 8. The number of transverse seams VN and their spacing from eachother may also be varied depending on the requirements of the modulemanufacturer.

For assembling the webbings having the various portions as justdescribed they are installed in the retraction portion ARB orientedtowards the retractor whilst the other end with the inflation portionABB is joined to a gas supply. Details of this are known from prior artand thus do not need to be described in the present specification.

Referring now to FIG. 9 there is illustrated an adapted woven webbinghaving a middle part M, right outer parts RA1, RA2 and left outer partsLA1, LA2 which as shown in FIG. 10 depicting a woven two-ply webbing(strongly schematic) in cross-section, is folded in the sequence of thearrows U1, U2 so that in the end they are located on the top or bottomside of the middle part M. The further steps in the method are the sameas those as already described for the example embodiments above.

Indicated by the broken line in FIG. 9 is the outer contour of thewebbing furnished by the weaving machine. The thick enveloping line 50in the region of the outer parts marks the nip seams as described above.The shaded portion between the outer contour and line 50 is cut out,details of which are analog to that as shown in FIG. 6. In principle,all configurations of the “cut-out” belt bag webbing width are possible,e.g. for a large volume in the head portion, “near zero” volume in theregion of the buckle, etc. Each version is harmonized to customerrequirements.

The left-hand end of the webbing as shown in FIG. 9 comprises a portion100 which is inflated when required in the region of the head of thevehicle occupant whilst the right-hand end contains a portion 200smaller in cross-section as compared to that of the portion 100 which islocated and inflated in the region of the chest and lap of the vehicleoccupant.

Referring now to FIG. 10 there is illustrated a webbing divided into thefollowing five sections: LA1, LA2, M, RA2 and RA1. The sections LA1 andRA1 are folded clockwise as shown by the arrows U1 through roughly180·(in FIG. 10) and located on the sections LA2 and RA2 respectively.Each of the “packages” LA1/LA2 and RA1/RA2 is then folded onto themiddle part, thus resulting in the individual sections being concertinafolded. Further handling of the webbing is analog to the webbing versionalready described with three sections. In accordance with the inventionand depending on the requirements it is also possible to provide furtherouter parts LA3, LA4, . . . RA3, RA4, . . . (seven sections, ninesections) to tailor the volume of the inflated air bag belt to theindividual requirements in each case.

What is claimed is:
 1. A method of fabricating an inflatable webbingmore particularly for a seat belt, comprising the steps of: 1.1 weavinga two-ply fabric having an upper ply and a lower ply, comprising a) thefabric including at least one left outer part, a middle part, and atleast one right outer part, roughly equal in width, b) the warp threadsof the outer parts are finer than the warp threads of the middle part,c) in the narrow creases, each located between the middle part and theadjoining outer parts, opposite the broad middle part the warp threadsare finer than the warp threads in the middle part, but coarser tan inthe outer parts, d) the upper ply and the lower ply are interwoven inthe region of the outermost edges of the outer parts, e) the upper plyand the lower ply are interwoven at least in the region of the twonarrow creases with at least one burst tread running substantially inthe warp direction, 1.2 folding and placing the outermost outer parts onadjoining parts so that all parts are located in sequence above or belowthe middle part to result in, as viewed in the warp directions theconfiguration of a collapsed concertina, 1.3 tucking the middle part tothe left so that the upper ply and the lower ply of the middle partformerly facing each other now face outwards and sandwiching the foldedouter parts and the middle part in between.
 2. The method as set forthin claim 1, in which the two-ply fabric has the following designfeatures: a) the fabric webbing width is divided into three partsroughly equal in width, namely a left outer part, a middle part, and aright outer part, b) the dtex of the warp threads of the outer parts isthat of warp threads as usual for airbags, more particularly, a dtex ofapproximately a tenth of the dtex of the warp threads of the middlepart, c) in two narrow creases, each located between the middle part andthe adjoining outer parts, the warp threads are finer than the warpthreads in the middle part, more particularly, having a dtex roughlyhalf that of the warp threads of the middle part, d) the two fabricplies are interwoven in the region of the outermost edges of the outerparts, e) the two fabric plies are interwoven at least in the region ofthe two narrow creases with at least one burst thread runningsubstantially in the warp direction.
 3. The method as set forth in claim1, characterized in that the two fabric plies in the middle portion ofthe middle part are interwoven with at least two burst threads runningin the warp direction.
 4. The method as set forth in claim 1,characterized in that the fabric is coated on the outside prior to beingfolded.
 5. A webbing, more particularly for a seat belt, comprising awoven two-ply fabric having an upper ply and a lower ply comprising: a)the fabric webbing width is divided into three parts roughly equal inwidth, namely a left outer part, a middle part, and a right outer part,b) the warp threads of the outer parts are substantially finer then thewarp threads of the middle part, c) in relation to the middle part,narrow creases each located between the middle part and the adjoiningouter parts the warp threads are finer than the warp threads in themiddle pan, but coarser than in the outer parts, d) the upper ply andthe lower ply are interwoven in the region of the outer most edges ofthe outer parts, e) the upper ply and lower ply are interwoven at leastin the region of the two narrow creases with at least one burst threadrunning in the warp direction, f) the left outer part is folded alongthe left crease onto the upper ply of the middle part, g) the rightouter part is folded along the right crease onto the lower ply of themiddle part, so that, viewed in the warp directions the configuration ofa collapsed concertina materializes, h) the middle part is tucked to theleft so that the upper ply and the lower ply of the middle part formerlyfacing each other now face outwards and sandwiched the folding outerparts and the middle part in between.
 6. The webbing according to claim5, wherein the one or both burst threads running in the two narrowcreases are woven or stitched.
 7. The webbing as set forth in claim 5,characterized in that the fabric is coated on the outside.
 8. Thewebbing as set forth in claim 5, characterized in that the weft threadis made of a monofil and/or multifil.
 9. The method as set forth inclaim 1 for fabricating a webbing woven to specification, wherein: thestep “1.1 weaving a two-ply fabric” is implemented such that the two-plyfabric comprises the following further features: 1.1 f) the fabric isdivided into two portions differingly woven in part, namely a retractionportion of the webbing and an inflation portion of the webbing, g) theupper ply and the lower ply of the outer parts of the webbing areinterwoven by means of transverse seams in the weft direction along apredetermined strip between the retraction portion and inflationportion, h) the upper ply and the lower ply of the outer parts of thewebbing are interwoven by means of longitudinal seams in the warpdirection along strips running directly along strips running directlyalongside the creases in the retraction portion, prior to the step “1.3Tucking the middle part” the following step is implemented: 1.31 cuttingout the outer parts each divided from the remaining webbing by the wovenlongitudinal and transverse seam.
 10. The method as set forth in claim1, characterized in that after the step “1.3 Tucking the middle part” ofacut-to-length piece of the webbing the following steps are implemented:1.5 inserting an end portion of a certain length of a single-ply webbingbetween the upper ply with outer part and lower ply with outer part ofthe two-ply fabric, 1.6 stitching the sandwiched upper ply of the middlepart with outer part, end portion of specific length of single-plywebbing, lower ply of the middle part with outer part by means of one ormore seams spaced away from each other sufficiently so that theoverlapping portion of the plies remains floppy.